#include <stdio.h>
int main() 
{
	int n;
	double fz=2,fm1=1,fm2,sum;
	scanf("%d",&n);
    for(n;n>0;n--)
    {
    sum+=fz/fm1;
    fm2=fz;
	fz=fz+fm1;
	fm1=fm2;
	}
	printf("%.2f",sum);
}
